The use of re-closable flexible pouches has seen dramatic increase in the last few years. Heretofore the primary market for bags with slider zippers has been consumers who purchase empty slider bags and then fill the slider bags with products at home. However, with the increasing popularity of slider bags most manufacturers now tend to package their food and non-food products in slider bags for sale to consumers. The slider bags are a great convenience to the consumer who purchases these product filled bags especially for products of the type where only a portion of the product is used at any given time. The product applications for which slider bags may be used are virtually unlimited.
Plastic bags having zipper closures typically consist of two substantially similar sized sheets of plastic film (usually supplied from a pair of continuous web spools or rolls) which are then sealed together at a lower end of the sheets to form a front layer and a rear layer, with the seal forming a bottom edge of the bag. Alternatively, the plastic bag may be formed by a length of bag film folded upon itself to form a front layer and a rear layer connected by an integral bottom edge defined by the fold. Side edges of the plastic bag are typically sealed using a sealing head.
The typical slider bags that are being manufactured are airtight as far as solids and powders are concerned. However, the bags are neither leak proof nor drip free where liquids are concerned. The problem of leakage is two fold in that leakage occurs due to the improper sealing of the side edges and also due to improper design of the slider and zipper.
The zipper closure itself is airtight along its length due to the releasable and reusable seal formed by the inter-locked profile. A long standing problem in the art of zipper sealed plastic bags however has been the presence of escape gaps which are created during heat sealing at the outermost edges (such as at the bags two side seal locations) of the zipper closure. A drawback of such a method of sealing is the escape gaps that are formed at the intersection of the zipper closure, the bag film, and the side edges of the plastic bag. These escape gaps are frequently formed as a result of applying continuous pressure and heat to seal the side edges of the bag, without making accommodations for the underlying zipper closure that is typically already sealed along the top edge of the bag film. Such escape gaps facilitate leakage of air and/or liquid directly into or out of the contents of the plastic bag, which can cause undesired spillage, contamination and spoilage of such contents.
U.S. Pat. No. 3,986,914 and U.S. Pat. No. 6,033,113, incorporated here in totality by reference, address this problem and have provided methods of overcoming this drawback. U.S. Pat. No. 3,986,914 provides for a plastic bead seal at the junction of the interlocking fastener and the side edges of the container. The plastic bead seal formed by a pressure bar, acts as a barrier to the passage of fluids or contaminating bacteria through the fastener at this junction. One drawback of the method of providing bead seals is that the bead seals are formed as a separate step in the manufacturing process. Also, the pressure bar with the specially configured channel is not found on conventional bag making machinery.
U.S. Pat. No. 6,033,113 provides for a zipper closure that is provided with fillets along the uppermost and lowermost interlocking fingers of the zipper to prevent escape gaps from forming between the two sides, especially at the bags side seal locations. Conventional heat dies are used in combination with excess quantities of plastic material to form the fillets. The method of fillets involves the use of extra plastic materials for the fillets.
To overcome this problem of escape gaps in particular at the side edges, the invention provides for the use of a sealing head with grooves made on their inner surfaces such that excess material may flow into the grooves of the sealing head and not result in escape gaps being created during the cooling stage. This may be better understood with reference to FIG. 16, wherein the grooved edges are shown (35).
The slider device typically includes a separator or plow-type structure in the middle, or at one end, that opens a zipper closure mechanism having male and female interlocking profiled elements or closure profiles when the slider device travels in a first direction along the zipper closure. The sidewalls of the slider device are inwardly tapered from one end to the opposite end so that the sidewalls engage the closure profiles and progressively move them into engagement to close the re-closable package when the slider device is moved along the zipper closure in a direction opposite to the first direction.
Re-closable packages that include a slider device to more easily open and close the profiles typically face problems in providing a liquid tight seal across the entire length of the zipper closure due to the fact that the slider includes a plow device used to separate the closure profiles as the slider is moved along the length of the zipper closure. Thus a portion of the zipper closure beneath the plow remains open at all times. One way of solving this problem is to include a notch formed in the mating profiles above the inter-locking elements to define a home position for the slider when the package is in the completely closed position. The notch formed in the profile typically receives the plow formed on the slider such that the profile can be closed on each side of the plow to create a continuous seal across the entire package. Typically, the plow of the slider device does not extend past the inter-locking elements such that the notch does not create an opening between the inter-locking elements formed on the closure profiles.
Although the notch formed in the mating profile on the closed end of the re-sealable package is known, problems can occur in utilizing such a notch with a full-length plow. For example, during the formation of the notch portions of the re-sealable package near the location of the notch can be damaged which affects the performance of the package.
U.S. Pat. No. 4,890,935 describes a slider wherein a foam plastic gasket material is positioned between the inter-locking profile elements of the zipper at the closing end of the pouch and sealed thereof. The opposite end of the gasket material is free and extends into the space between the profiles at the closing end of the bag. When the leading edge of the slider is brought into engagement with the gasket material a seal is formed thereby eliminating the gap which otherwise would form in the area occupied by the free end of the gasket. A slider tab is also provided on the slider to engage a hook at the end of the zipper closure to hold the slider in position and maintain the seal. This method though effective is not practical as the addition of the gasket material and hook not only increases costs but also involves an extra step in manufacturing. Furthermore closing of the pouch involves an extra step of hooking the slider tab to maintain the seal. These factors make this method unviable.
U.S. patent application 2004/0086206 provides for a seal region between the flaps of the male and female closures, such that the seal extends towards the center of the package from the edge and is of a pre-defined length. This pre-defined length of the seal is greater than the length of the slider. The seal region therefore provides a fluid tight seal between the two sealed flaps and below the slider when the slider is in the home position. Theoretically the method of preventing leakage at the ends of the zipper as described by U.S. 2004/0086206 appears to meet its objective. However, experimentation has found that liquid tends to seep into the gap between the seal and the zipper and leak out through the gap in the zipper profile at the end edge due to the plow. Further, the method also involves the use of extra sealing material as well as an extra manufacturing step that adversely affects costs.